Monitoring line conditions, disturbances, and faults is essential to ensure proper operation of a power system. Autonomous wireless sensors are key elements which can enable such monitoring in a simple, easy and cost effective manner. Such sensors can probe the necessary currents, voltages, and insulation properties of a power line in a non-intrusive manner and then relay such data to a decision station wirelessly. Sensors exist which require power of 10 mW. Low power wireless sensors can rely on high capacity batteries to operate for years. However, to keep the sensor size and cost to a minimum, the energy needs of sensors can be met by miniature cheap batteries (e.g. coin cell batteries). Since smaller batteries have limited capacity they must be recharged from time to time.
A good option for solving the energy needs associated with wireless sensors is to scavenge energy from the ambient environment. This may include scavenging energy using solar, vibrational, thermal, acoustic and electromagnetic mechanisms. A variety of mechanisms have been utilized in this regard, including photovoltaic technology specifically applicable to indoor lighting environments, moving magnets through a coil and a spring for a resonant structure so vibrational energy could be converted, scavenging power from human movement, thermoelectric devices that can produce power from a temperature differential, and electromagnetic generators.
Wireless power transfer by EM induction has been investigated by many researchers for various applications. The principle of inductive coupling for wireless power transmission has been utilized but the mechanisms to date are either unsuitable for real world implementation or cannot provide enough power. A comparable (but not identical) structure is a Rogowski coil. However, if a small Rogowski coil is used, it will harvest very low power because of its material construction which contains an air core. The induced voltage is so low that an active integrating device will be needed to enhance that voltage. The active integrating device itself will consume energy. On the other hand, a large size Rogowski coil will not be convenient for certain applications, such as most miniature sensor devices. If they are used with a large number of wireless distributed sensors on an overhead power line their weight can easily create additional undesired sag.
Thus, improvements in mechanisms for scavenging energy are still needed.